Communication systems networks are many and varied in design. The particular application of one will call into play certain aspects of communication technology while another will rely on another way of solving its own problems. Irrespective that a highly complicated multiplex system or a single wire, two-party communicator is involved, each can be modified to vastly increase their capabilities.
Audio communication systems among which several users share a common transmission bus or data link are in widespread application. These can be as complex or simple as their intended use and generally have microphones and loudspeakers at user-terminals. Probably one of the most well known, typical terminals is a mobile citizen band transceiver. Another is the conventional telephone receiver which restricts the conversation between parties holding their headsets next to their ears and mouths. Modifications or combinations of the transceiver and the telephone have been tried to enable the monitoring of network conversations and to have a degree of privacy for calls to and from the network.
One such attempt was tried by A. B. Simpkins in his U.S. Pat. No. 3,114,800. An attachment was added for a telephone handset that encoded and decoded information among a number of users. The modified handset had to be hand held and suitably actuated to perform as expected and had no capability for allowing one or a number of users from monitoring all system traffic. A later design by S. M. K. Horn et al appearing in U.S. Pat. No. 3,321,580 disclosed a hands-free communication system including certain privacy features. Microphone loudspeaker combinations were responsive to a pair of signal tones for actuating microphones or loudspeakers at opposite ends or along receiver terminals in the communications link. This enabled a bit of selectivity among users. U.S. Pat. No. 3,497,623 to B. F. Todd discloses a device for securing telephone conversations that mixes loudspeaker projected noise along with voice in a microphone. The secured communication system allows two or more persons to communicate without the possibility of being overheard by eavesdroppers or concealed recording devices. The speaker is for projecting noise for blanketing speech at a conventional telephone handset. A later effort by W. C. Doyle et al in U.S. Pat. No. 3,541,258 discloses a conference communication system. Earphones and cranial microphones induce speakers to speak in a lower volume so that prerecorded sounds can mask communications between designated users. A selectivity between simply monitoring a network's communication with the option to interrupt and contribute or monitor on a more secure basis is nominal.
Joseph Hallaby in his U.S. Pat. No. 3,718,765 modified a telephone communication system with noise signals that are alleged to provide for a degree of secrecy. A number of noise generators strategically located throughout the system help provide improved secure communications; yet, the option for open and free monitoring along with secured communication through a handset is not found. In like manner, James W. Crimmins, U.S. Pat. No. 3,775,562 shows a noteworthy step forward in the state-of-the-art for assuring a secure telephone communication system; however, certain situations could make a hands-free capability an advantageous modification.
Thus there is a continuing need in the state-of-the-art for a communication system joining a number of users that allows an optional hands-off monitoring and a secure bidirectional communication that does not overly compromise the system's reliability.